BccList is a TIdEMailAddressList property used to store email addresses for recipients that will receive a carbon copy of the message, but do not appear in the RFC 2822 message header "To:" for the message. 

BccList is often used for mailing list applications, where members of the mailing list should receive a copy of a message addressed to the list. 

Use Recipients to identify email addresses included in the RFC 2822 message header "To:". 

Use CCList to indicate additional message recipients that may appear in the RFC 2822 message headers for the message.

(Delphi) Updating a list of email addresses 

  AMessage.CCList.EmailAddresses :=
  '"John Doe" <jdoe@some.net>, "Jane Doe" <janed@another.net>';

  with AMessage.BCCList.Add do
  begin
    Name := 'John Doe';
    Address := 'jdoe@some.net';
  end;

  with AMessage.BCCList.Add do
  begin
    Name := 'Jane Doe';
    Address := 'janed@another.net';
  end;

TIdEMailAddressList 

TIdEMailAddressItem 

TIdMessage.CCList 

TIdMessage.Recipients